This invention relates generally to garage door openers, more particularly to remotely controlled systems for opening and closing garage doors, gates and the like, and even more particularly to systems of this type which provide increased security from unauthorized access.
The use of remote control systems to operate barriers, such as garage doors, gates and the like, is well known. Such remote control systems typically utilize hand held transmitters which emit encoded signals transmitted at radio frequencies to a receiver associated with an automatic door or gate operator. The receiver is effective to intercept and decode the transmitted signal and thus cause the actuation of the operator to open or close the door or gate. These systems include the type in which the receiver has code switches which can be manually set to correspond to the authorized transmitter codes or, alternatively, may be xe2x80x9clearnxe2x80x9d type systems in which codes or the like used to identify authorized transmitter codes are initially stored in the receiver during a preparatory program or learn mode.
The risk of unauthorized access is a major concern associated with the use of the above mentioned systems. For example, unauthorized access can potentially be achieved by means of an exhaustive, systematic search in which a large number of different codes are successively transmitted in the hope that, eventually, one of the transmitted codes will match the authorized code and activate the system. Another scheme used to gain unauthorized access is a technique, sometimes referred to as xe2x80x9ccode grabbingxe2x80x9d, in which the initial transmission of the authorized code is electronically intercepted and stored for later unauthorized use.
Many of the prior art remote control systems have been susceptible to unauthorized access by one or both of the above described methods. For example, U.S. Pat. No. 4,750,118 issued Jun. 7, 1988 to Heitschel et al. discloses one type of xe2x80x9clearnxe2x80x9d remote control system for operating a garage door opener, but one particularly susceptible to code grabbing, in that each transmitter unit of the disclosed system has its own unique, but non-changing code. Accordingly, since each transmitter unit sends the exact same coded signal to activate the door operator every time it is used, the system of the Heitschel et al. patent is vulnerable to having the code intercepted and later used to gain unauthorized access.
The system of the type disclosed in the Heitschel et al. patent has additional disadvantages which inhibit its effectiveness. For example, the means used to transfer between the program (learn) mode and the operate mode comprises a two-position mechanical switch disposed on the operator power head housing suspended from the garage ceiling, and which must be manually moved between program and operator positions to place the receiver in either the xe2x80x9clearnxe2x80x9d or xe2x80x9coperatexe2x80x9d mode. Moreover, the means used to enable receiver storage of codes from different transmitters is also a multi-position mechanical switch which must be manually moved to the desired position prior to receipt of the particular transmitter code. Such arrangements are awkward and inconvenient and, as will be appreciated by those skilled in the art, potentially unreliable.
Barrier (garage door or gate) control systems which use a technique known as code hopping or code stepping are also known and have been previously described and used as a means for preventing unauthorized access by so-called xe2x80x9ccode grabbingxe2x80x9d. In accordance with this code hopping technique, the code that activates the system changes (i.e., steps or hops) after each use. For example, one particular advantageous form of code hopping is described in U.S. Pat. No. 5,517,187 to Bruwer et al., assigned to an assignee of the present invention. However, a code hopping technique in accordance with the present invention as well as the manner by which it is incorporated with the design and operation of the remote system itself, uniquely distinguishes the total system of the present invention from prior art systems.
Accordingly, a need for further improvements in remote controlled door and gate operator systems has continued to be felt.
It is therefore a principal object of the present invention to provide a new and improved remote control door and gate operating system. Another object is to provide such a remote control operating system with improved means for preventing unauthorized access, including code grabbing. A still further object of the invention is to provide such a system which avoids the disadvantages and inconveniences associated with prior art systems utilizing mechanical or manually actuated switches.
Other objects and advantages of the invention will become apparent from the following specification, accompanying drawings and claims.
In accordance with a key feature of the present invention, a form of code hopping embodying a unique sequential decryption/comparison technique is incorporated into the operation of a remote control system for activating barrier opening apparatus, particularly garage door or gate openers. In addition, the remote control system is of a xe2x80x9clearnxe2x80x9d type, but one in which the authorized operating codes stored in the receiver during the learn mode are never themselves transmitted from the transmitter.
Broadly stated, the remote control system of the present invention comprises one or more RF transmitters and a digital type RF receiver associated with the door operator. The receiver is initially programmed with a xe2x80x9cmanufacturer""s keyxe2x80x9d value. Every system produced by a given manufacturer has the same manufacturer""s key. In addition, each transmitter is initially programmed with a unique serial number and unique xe2x80x9csecret keyxe2x80x9d. The secret key stored in the transmitter is generated using the unique serial number of the transmitter and the manufacturer""s key. Thus, every transmitter has a different serial number and a different secret key. When the transmitter is activated, it performs a nonlinear encoding function using the secret key to generate a changeable hopping code signal. The hopping code changes (i.e., hops) every time the transmitter is activated.
The transmitter""s unique secret key is never transmitted, and although the transmitter""s unique serial number is transmitted, it is not stored in the receiver. In accordance with a feature of the invention, the secret key value which is stored in the receiver is self-generated in response to the encoded transmission from the transmitter during the program or learn mode of the receiver. During the subsequent operate mode, the receiver then uses the previously generated and stored secret key to decode the hopping code signal from the transmitter. The door operator or opener device is activated when such decoded information is within a xe2x80x9cwindowxe2x80x9d or range of acceptable values as determined by a sequential comparison technique subsequently described.
In accordance with other unique features of the system of the invention, the transition of the receiver between the operate mode and the learn mode is effected by means which momentarily places a microprocessor associated with the receiver in the learn mode, followed by the automatic return of the microprocessor to the operate mode without any further action required of the user. In addition, the system of the present invention enables a technique of random storage in unused receiver memory to accommodate codes from different transmitters rather than requiring the receiver to be xe2x80x9cswitchedxe2x80x9d to a different memory location for a given transmitter.